The present invention relates to rotary valves designed for use with Gerotor rotary machines which are used as fluid pumps or motors in which the fluid introduced is contracted and expanded by a meshing gear system generally known as a Gerotor, and more particularly the invention relates to a rotary valve including sealing means designed to prevent leakage of fluid between the high pressure side and the low pressure side of the commutator.
With a fluid motor or pump of the Gerotor type in which a rotor formed with one less external teeth than the number of internal teeth of a stator, is rotated in eccentric mesh with the stator and a plurality of expanding and contracting cavities are defined by the teeth of the stator and the rotor in response to the eccentric rotation kf the rotor, it has been the practice to use a rotary valve so as to selectively communicate the fluid passages with the Gerotor cavities so that a hydraulic oil is supplied to impart a turning force to the rotor in the case of a fluid motor, while a hydraulic oil is discharged from the contracting Gerotor cavities in the case of a fluid pump.
With a known rotary valve of this type, due to the fact that the commutator is rotated within the valve chamber, a clearance which is as small so as not to impede the rotation of the commutator is provided at each side of the commutator, and consequently there is a disadvantage that the oil tends to leak from the high pressure side to the low pressure side within the valve chamber, thus deteriorating the volumetric efficiency of a motor or pump. As a result, the width of the clearance on each side of the commutator has been made very small so far as the rotation of the commutator is not impeded, thus requiring a high degree of finishing accuracy for the component parts of the rotary valve. However, there is a disadvantage that even if the component parts with a high degree of finishing accuracy are used, the clamping force of bolts or the like used in assembling the valve tends to distort the component parts of the valve chamber and moreover the existence of the high oil pressure portion and the low oil pressure portion within the valve chamber tends to similarly distort the component parts of the valve chamber by the pressure difference between the two portions, thus increasing the width of the clearance at each side of the commutator. This condition may be aggravated when thermal expansion occurs in use causing mechanical seizure of the parts.
It has been further found that upon continued operation of the Gerotor unit, and resultant thermal gradients will cause dimensional expansion which will cause binding, seizure and surface scoring of the commutator.
In U.S. Pat. No. 3,452,680, it has been proposed that a sealing element be interposed between the casing or housing and the commutator. Although such an arrangement provides a seal, it has the disadvantage in that the continuous movement of the seal element relative to the casing causes wear on the sealing element requiring maintenance, repair and replacement.
In U.S. Pat. No. 4,449,898, a solution to the aforementioned problems was proposed wherein the commutator comprised two spaced members movable in unison with a sealing element interposed between the two members.
In practice, it has been found that such a fluid motor operates satisfactorily for unidirectional operation. However, when input flow was reversed, it has been found that there is improper axial pressure balance and may result in insufficient sealing.
Accordingly, among the objectives of the present invention are to provide a rotary valve for a Gerotor type fluid rotary machine wherein the axial sealing forces are pressure balanced or biased to minimize the slippage volume and improve the volumetric efficiency, minimize the coulomb friction and improve the mechanical efficiency, provide proper break-away torque characteristics for rotation in either direction, which will make the axial separating force less dependent on the compression of an elastomeric seal; which will permit the application of the fluid motor in hydraulic systems with overrunning loads; and which will make the rotating/orbiting disc more tolerant to thermal shock; which can be manufactured readily by the utilization of conventional manufacturing techniques.
In accordance with the invention, the commutator comprises circumferentially spaced pairs of sealing rings adjacent the outer and inner periphery of the two spaced members.